OK, you demonstrated that you poorly understand what is referencing the DLL, thank you. Essentially, you reference assembly, no "DLL", which is meaningful in .NET (just a file type). What is "reference a class"? OK, did you add the System.Management reference?
—SA

This is because you declare "wmiClass" and spelled "cmiClass" below. Come on, Visual Studio points it out precisely. You need to learn how to read it. And please, read the chapter on .NET assemblies. This is one of the most fundamental things.
—SA